This invention relates to a method for casting-in or impregnating electrical components and for casting with epoxy resin compositions.
As is well known in the art, casting and impregnating resins, such as epoxy resins, harden faster at higher temperatures than at lower temperatures. Hardening at low temperatures is possible only in the presence of basic catalysts, particularly aliphatic and aromatic amines.
Reactive epoxy resin compositions used for casting-in and impregnating, filled and not filled, should have low viscosity for the manufacture of moldings, so that good impregnation is obtained. The desired low viscosity can be obtained by using low-molecular weight components, low-molecular weight reactive and nonreactive substances or also by employing the given resin compositions at a higher temperature, i.e. by the viscosity reduction which sets in with increasing temperature.
However, low-molecular components of the epoxy resin compositions, for example, reactive thinners such as butane dioldiglycidyl ether, cresylglycidyl ether, phenylglycidyl ether and butylglycidyl ether, cause high reaction shrinkage during hardening, which is usually accompanied by a strongly exothermic heat reaction, and the moldings obtained are brittle. Low-molecular non-reactive components such as solvents, softeners and the like can cause additional shrinkage in the molded articles due to evaporation, porosity, tension cracks, migration, poor temperature aging behavior, etc. While the viscosity of the composition is lowered by the process-related measure of increasing the temperature, the increase in the speed of the reaction connected therewith makes the viscosity of the composition increase rapidly, whereby the processing time of the compound is shortened.
It is known to use tertiary amines such as triethanol amine, benzyldimethyl amine and 2,4,6-tris-(dimethylaminomethyl)-phenol as hardening agents for polyepoxides and as accelerators in the hardening of mixtures of polyepoxides and polycarbonic acid anhydrides at elevated temperatures.